1. Field of the Invention
The present invention relates to percutaneously absorbable formulations such as analgesics such as morphine, or its salts or bases.
2. Background of the Related Art
Narcotic analgesics such as morphine or its salts and nonnarcotic analgesics such as eptazocine have been orally administered or injected to ease postoperative and cancerous pains.
In the case of such injecting agents, at-home treatment is difficult because of the necessity of administration by a third person, and further medicines having short working times such as morphine are disadvantageously difficult to administer at the time of acute pain because of its increased administration frequency.
Oral agents, which have been developed for the purpose of simplification of administration and use, overcame some disadvantages of the injecting agents, but are not so much improved in working time, in which the migrating property and retentivity of the formulations in digestive organs are difficult to control even by pharmaceutical designs for gradual release, and the persistency has its limit.
Further, many cancer patients in the last stage can not have oral administration of analgesics because of vomiting and nausea which are the side effects of carcinostatic substances.
On the other hand, formulations applied to the skin have an expected persistency of medicinal effect of about 24 hours to 1 week for one administration, and are applicable to patients for which oral administration is not possible.
In general, medicines have low percutaneous absorbability, and it is the same with analgesics including morphine and its salts.
The main barrier to percutaneous absorption of medicines resides in a horny layer, and various accelerators have been developed as the accelerators were considered to increase the percutaneous absorbability to the lipids of the horny layer. However, the medicine permeability of the epidermis other than the horny layer becomes the barrier in simple absorption accelerators acting on the horny layer and combinations thereof, so that very excellent accelerators have not been developed yet.
In view of the disadvantages of the prior arts, as a result of the earnest studies on utilization of analgesics such as morphine, which were used only as injecting agents and oral agents in the past, for percutaneously absorbable type external agents such as ointment, cream, tape dressing, plaster dressing, patch dressing, and pap dressing (wet dressing), the present inventors have found and attained this invention.